🎨 Palette: Add aria-label and title to remove attachment button

[thirdeyenation]

💡 What: Added an aria-label and title attribute to the remove attachment × icon-button in inputPreview.html.
🎯 Why: The button only displayed a × character, which screen readers often misinterpret (e.g. "multiplication sign" or just "times"). Additionally, mouse users lacked a tooltip indicating the button's action. This makes the UI more accessible and intuitive.
📸 Before/After: Not applicable (invisible UX change / tooltip addition).
♿ Accessibility: Screen readers will now announce "Remove attachment" instead of "times", and keyboard users navigating to the button will get appropriate context.

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PR created automatically by Jules for task 17889777414443743388 started by @thirdeyenation

[google-labs-jules]

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